# ELF magnetic field survey

> A source-finding walkthrough plus a 24-hour log, because power-frequency magnetic fields track electrical load and a spot reading answers almost nothing.

- Canonical URL: https://emfbase.com/protocols/elf-magnetic-survey
- Collection: Measurement protocols
- Record id: `protocols:elf-magnetic-survey`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/protocols/elf-magnetic-survey
- Also known as: how to measure milligauss, gaussmeter survey

## Key values

- **Quantity measured:** magnetic flux density

## Goal

Find the source of any elevated 50/60 Hz magnetic field and quantify exposure at sleeping and working positions over a full day.

## Equipment

- ELF gaussmeter (power-frequency magnetic field)
- Logging EMF instrument

## Procedure

1. Record meter model, axis configuration and frequency response.
2. Walk the perimeter of each room with the meter at waist height, noting every local maximum and its apparent source.
3. Measure at 0.3 m, 1 m and 3 m from each candidate source to confirm the inverse fall-off that identifies a compact source.
4. Check the service panel, meter base, and both sides of every wall that backs onto one.
5. If readings are elevated everywhere and do not fall off with distance, suspect net current on the neutral or a shared neutral, and involve an electrician.
6. Log continuously for at least 24 hours at the pillow position, sampling at least once per second where the instrument allows.
7. Report the mean, the night-time mean and the 95th percentile, not just the maximum.

## Pitfalls

- Spot-reading at one time of day, when line and household loading vary by several times
- Using a single-axis meter and rotating it inconsistently
- Assuming shielding is the fix; magnetic fields pass through nearly all common materials
- Missing a wiring fault, which is the one cause that raises the whole building and cannot be solved with distance
- Using a 50/60 Hz-only meter near inverters, EV chargers or induction hobs, where the energy is in the kilohertz range

## Interpret results against

- Building Biology SBM-2024 AC magnetic field bands
- WHO/IARC ELF magnetic field association threshold (0.3–0.4 µT)
- ICNIRP 2010 general public magnetic field reference level at 50/60 Hz
- Swiss installation limit value for power lines

## Related records

- [Electrical service panel and meter base](https://emfbase.com/emitters/electrical-service-panel): The highest-current point in a building: readings in the tens of milligauss are normal within a metre, falling to background within two to three metres.
- [ELF gaussmeter (power-frequency magnetic field)](https://emfbase.com/meters/elf-gaussmeter): Measures 50/60 Hz magnetic flux density in milligauss or microtesla — the instrument for wiring faults, service panels, transformers and power lines.

## Sources

- `sbm-2024` Institut für Baubiologie + Nachhaltigkeit (IBN) (2024). *Building Biology Evaluation Guidelines for Sleeping Areas (SBM-2024)*. https://buildingbiology.com/site/downloads/SBM-2024_EVALUATION_GUIDELINES_EN.pdf — ngo, link checked 2026-08-12
- `niehs-emf` National Institute of Environmental Health Sciences. *Electric and Magnetic Fields*. https://www.niehs.nih.gov/health/topics/agents/emf — government, link checked 2026-08-12
- `who-elf` World Health Organization (2007). *Electromagnetic fields and public health: exposure to extremely low frequency fields*. https://www.who.int/teams/environment-climate-change-and-health/radiation-and-health/non-ionizing/exposure — government, link checked 2026-08-12

Data licence: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Dataset version 2026.08.1. Retrieved from EMFBase, https://emfbase.com.

This record is reference data, not medical or legal advice. Regulatory limits, scientific guidelines and precautionary values are labelled separately and answer different questions.